Television pickup tube



Jan. 26, 1954 G, B GQFF 2,667,6QQ

TELEVISION PICKUP TUBE Filed Nov. 27, 1951 Inventor @wrws %xzm-ma Fnnuus Gonltorney Patented Jan. 26, 1954 2,567,600 TELEVISION PICKUPTUBE qrse Be nar Goff, C mbr d e, England, a

s lgnor to .Gathodeon Limited, Cambridge, Engand, a British company Application Novembenz'l, 1951, Serial No. 258,347 5 .Qlailns. (Cl. 31,5 1 1) pre ent inv ntion relates to television face, but so that the ,CDlleutqr; coating isinteriek ll tu s. andls an mprovementin or medi pos d, on. the envelope wall. between the stora li ation of the invention formin the subject of surface and the photoensitive"coating, ndn eopending patent application Serial No. 163,658, annular light source-r annular, array or grou now Patent No. 2,622,226. of light sources is ar anged aroundthe envelope n the c fi ati n f h bov application for illuminating the photo-sensitivecoating th disclosed a method and means for improving collector electrode heing arranged to be mainthe operation of pick-up tubes of the kind emtained at a positive potential; relatively to; the:

such tubes of the image icon oscope tyne, by .re- 19 electrons, released froln the photosensitive coat? leasing photo-electrons from a suitably illumiing towards the,storage;surface.v nated photo-sensitive surface in the vicinity of According to a feature; of the-invention; in at so as to strike it with such velocity as to cause con in n the o agefill f-f lq c ld hhbtocafi emission frQln. the storage surface of secondary respectively,, which are. connected by an intere electrons in such ratio to the incident photomediate cylindrical neclr portionflof reduced'dicollector electrode being interposed between the wardsthe storage surface.

stora e and the photoc-sensitiyesurfaces andhe- The i lumination of thezphoto-sen i ive 00at-= ing maintained at a positive potential relatively in hould be such that thewhole-of the stora e to the photo-sensitive surface. In the embodis u fa is irradiated with t e phot lectronslnent of tube described, the photo-sensitive sur Ifhe illumination may be substantially uniform ele trode, also of annular form, is mounted 013- 33 storage urf How v r, the nt n ity: and/or posite the photo-sensitive coating, and by reason distribution of illumination ay be made adortha-t. arrangement the collector electrode is of justable to enable the intensity and distribution a perforated;construction in the form of a coarse Q1. th photo-emission and. charginaof 'th o mesh in order to allow the photo-electrons rea urface to b c n r lled: and ju d s:

lease -from the photo-sensitive coating to reach d r f rably s v ral lamps, such as of thestorage surface through the perforations in h pe nut f WD S; ar p ed the collector. around theenvelopatogetherwith means such- Aeeording to the-present invention both the as potentiometers or switches for controlling the;

trode are provided in therorm of annular in- 40 time r adjust n th ntensity and/or dist i collector coating being interposed, on the en- According to afeature of the'nr sent inven-- velope wall, between the storage surface and.the. P1011, 1n the a uf c ure f'ca u t-t ima e; photo-sensitive coating which is suitably spaced." 100110500138 type m d ing t is: invention, he-

from the storage surface for that purpose; photo-Sensitive di 1S f med-simultane usly envelope, and a collector electrode in the form from Q P a e c into the envelope in theenvelone in th vicinity of t sto a e sur thevicinity 0f the storagersurfacemhe two ata? aecmoo '3 o ings thereafter being simultaneously made photosensitive.

With an envelope having an intermediate neck portion as described, the material to be evaporated is introduced mto the end portion of the material is evaporated from there along the envelope so as to deposit; a coating on the remote end wall of the other end portion which is to contain the photocathode. In so evaporating the material, some part of the vapour is caused to be trapped by and to deposit a coating upon the above-mentioned corner or shoulder of the portion of the envelope containing the storage surface. I

In order that this invention may be more clearly understood, reference will now be made to the accompanying drawing which shows one specific embodiment thereof by way of non-limiting example. I

In the figure, which illustrates one mode of manufacture, the tube is provided with an antimony caesium photo-cathode. The tube has a main evacuated envelope 1 containing the target electrode comprising a charge-storage surface 2 and a signal plate 3 sealed into the tube with appropriate output lead 4. The target, as shown in the drawing, is mounted at one end portion of the tube which is also provided with an inclined side tube 5 containing a scanning-beam electron gun 6, the deflection coils "i and 8 being provided for the application as scanning potentials for causing the electron beam set up by the gun 6 to scan the target electrode in a conventional raster. The tube also contains a collector electrode 9 which is formed by depositing a ring of conductive material on the interior wall of the envelope l in known fashion in the vicinity of the target 2 and between the target and a shoulder it on the envelope 1 that forms a boundary between the end of the envlope carrying the target and a constricted opposite end portion.

The envelope is also provided with a small temporary side tube ll sealed to the portion of the envelope l containing the target electrode and positioned between the target and the shoulder Hi. This side tube H contains a slidable carrier l2 of magnetic material which carries at its lower end a predetermined charge 13 of material intended to form the base for the photo-cathode of the tube: in this case the material is antimony. The envelope has sealed to it also a further temporary side tube l4 containing a predetermined charge iii of caesium.

The side tube H has associated with it a magnet IG which may be an electro-magnet energised by a source of D. C. potential (I under the control of the switch it, as shown, or it may be a permanent magnet. The magnet is arranged so that it can control movement of the magnetic carrier 12 and therefore the magnet can be used to move the carrier containing the charge l3 of antimony into the envelope so that the charge [3 takes up the position shown at l3a.

By the application of heat, for example, by high-frequency induction methods or even direct electrical heating through suitable flexible leads, the antimony charge is caused to be evaporated through the constricted part of the envelope l to deposit a film of antimony on the far wall Hi, there to form a photo-cathode 2E), and also on to the shoulder H] of the envelope, there to form a coating 2!. After evaporation of the material, the carrier is removed by manipulation of the magnet is back into the side tube I, whereupon the latter is sealed-01f in close proximity to the main envelope wall without destroying the tubes vacuum.

The side tube M containing the charge of caesium is then baked whereby the caesium is distilled from the side tube 14, thus causing the caesium vapour to react with the deposited antimony to render the surfaces of the photo-cathode 20 and'the surface 2| light-sensitive. The side tube It is then sealed-01f and removed without destroying the vacuum of the tube.

The activated surfaces 20 and 2| may be then further sensitised by the addition of controlled amounts of oxygen.

In order to provide electrons for suitably biassing the target electrode, as above described, there is arranged an annular group of lamps 22 and reflectors 23 around the shoulder in of the envelope 1 that carries internally the photo-sensitive coating 2|. These lamps are connected to a suitable electrical circuit, the connections-of which are obvious and need not be illustrated.

Advantageously, the plurality of lamps 22 is controlled in groups by means of suitable variable resistors or the like whereby their intensity may be controlled so as to illuminate to a more or less degree any selected portion of the coating 2|.

If desired, the groups of lamps 22 may be replaced by an annular source of light in an annular reflector.

In order to enable the collector electrode to act as an accelerator electrode for the electrons emitted by the photo-sensitive surface 2|, it is held at a higher potential than said surface 2| and this is schematically illustrated in the drawing by the connection between those two surfaces of a source of potential 24.

In addition to the defects specifically discussed in application Serial No. 163,658, which television pick-up tubes of the kind in question sufier, such tubes have the further defect that the output video signal contains no components containing intelligence regarding the mean value of the light level of the light image. This is due to the requirement that, since the storage surface is insulated, the mean target current must equal zero over the frame period and, therefore, in order that any intelligence may be generated, it is necessary that the output signal waveform should include both positive and negative departures from this mean zero value. fore, the output signal is not uni-directional in relation to the zero value which is available as a reference during the line blanking period, it is not possible to use this reference level for purposes of D. C. restoration. However, by charging the storage surface negatively in the manner described herein and in the aforesaid application and, in particular, by effecting such negative charging during blanking periods of the scanning beam, and especially during the frame blanking periods, the storage surface may be biassed negatively sufiiciently to ensure, by reason of the fact that the mean target current must equal zero over the frame period, that the output video signal obtained during scanning is uni-directional in character, i. e., it contains D. C. components and hence information regarding the mean value of light level of the light mage being transmitted, thus facilitating D. C. restoration.

I claim:

1. A television pick-up tube of the image iconoscope type and comprising a storage surface and a photo-cathode spaced apart 1n parallel rela- 75 tion within the tube envelope, in which said envelope comprises two cylindrical end portions coating as an annular coating on said shoulder respectively containing the storage surface and facing substantially towards said storage surface, the photo-cathode, said first end portion being and a collector electrode in said first portion and of larger diameter than said second portion so also in the form of annular wall coating located that said end portion containing the storage sur- 5 between said photo-sensitive surface and said face has an internal annular corner or shoulder storage surface, means for illuminating said where it joins the second portion, a photo-sensiphoto-senstive surface, and means for maintaintive coating as an annular coating on said ing said collector electrode at a positive potential shoulder facing substantially towards said storage relative to said photo-sensitive surface whereby surface, and a collector electrode in said first 1c electrons released from said photo-sensitive surportion and also in the form of an annular wall face under the influence of light from said coating located between said photo-sensitive surillumination means are accelerated towards said face and said storage surface, means for illumistorage surface.

nating said photo-sensitive surface, and means 5. A television pick-up tube of the image for maintaining said collector electrode at a posil5 iconoscope type and comprising a storage surface tive potential relative to said photo-sensitive surand a photo-cathode spaced apart in parallel face whereby electrons released from said photorelation within the tube envelope, in which said sensitive surface under the influence of light from envelope comprises first and second portions resaid illumination means are accelerated towards spectively containing the storage surface and the said storage surface. photo-cathode, said end portions being connected A tube as Claimed in Claim prising together by a neck portion of smaller diameter means for adjusting the intensity and distribution tha the first said end portion containing the 0f Photo-emission from Said photo-Sensitive storage surface so that the said first end portion facehas an internal annular shoulder where it joins 3- A tube as c a m d n Claim in Which the the neck portion, a photo-sensitive coating as an illumination prises a plurality o Small 8160- annular coating on said shoulder facing substantric lamps arranged around said shoulder of said tially t d aid storage s rfa e, and an envelope, and means for Controlling Said lamps in annular collector electrode in said first portion any desired efl located between said photo-sensitive surface and 4. A television pick-up tube of the image Said stgrage surface iconoscope type and comprising a storage surface GEORGE BERNARD GQFF and a photo-cathode spaced apart in parallel relation within the tube envelope, in which said envelope comprises first and second end portions References Cited in the file of this patent respectively containing the storage surface and UNITED STATES PATENTS the photo-cathode, said end portions being connected together by a neck portion of smaller Number Name Date diameter than the first said end portion con- 2121356 Knoll June 1938 taming the storage surface so that the said first 2281638 sukumlyn May 1942 end portion has an internal annular shoulder 40 2368384 Schade 1945 where it joins the neck portion, a photo-sensitive 

